US Patent 7442409 Differential processing of powder coated substrates

A method of providing a powder coating to MDF substrate panels wherein, by the differential treatment of the front and back surfaces of these panels, both surfaces can be coated at the same time and the effects of moisture and other volatile outgassing is controlled in such a way as to provide a blemish-free front facing surface with a minimal, but nonetheless acceptable, amount of blemishes on the opposite or back surface. Differential treatment is achieved by preparing each surface using different grades of sand-paper, applying different amounts of curing energy, whether infra-red or thermal, or by applying different thicknesses of coating to each surface.